The present invention relates to golf balls and more specifically, to the use of segmented polyurethane materials in golf ball layers for improving golf ball physical properties.
Conventional golf balls can be divided into two general types or groups: solid balls and wound balls. The difference in play characteristics resulting from these different types of constructions can be quite significant.
Balls having a solid construction are generally most popular with the average recreational golfer because they provide a very durable ball while also providing maximum distance. Solid balls are generally made with a single solid core, usually made of cross-linked rubber, which is encased by a cover material. Typically, the solid core is made of polybutadiene which is chemically cross-linked with zinc diacrylate, and/or similar cross-linking agents, and is covered by a tough, cut-proof, blended cover. The cover is generally a material such as SURLYN(copyright), an ionomer resin produced by DuPont. Such a combination imparts a high initial velocity to the ball that results in improved distance. Because these materials are very rigid, two-piece balls have a hard xe2x80x9cfeelxe2x80x9d when struck with a club. Likewise, due to their hardness, these balls have a relatively low spin rate, which provides greater distance.
Wound balls typically have either a solid rubber or liquid center core around which many yards of a stretched elastic thread or yarn are wound. The wound core is then covered with a durable cover material such as ionomer or polyurethane. Wound balls are generally softer and provide more spin, which enables a skilled golfer to have control over ball flight. Particularly, with approach shots into the green, the high spin rate of soft, wound balls enables the golfer to stop the ball very near its landing position.
The design and technology of golf balls has advanced to the point that the United States Golf Association has instituted a rule prohibiting the use of any golf ball, in a USGA sanctioned event, that can achieve an initial velocity of 255 ft/s, when struck by an implement having a velocity of 143 ft/s (referred to hereinafter as xe2x80x9cthe USGA testxe2x80x9d).
Manufacturers place a great deal of emphasis on producing golf balls that consistently achieve the highest possible velocity in the USGA test without exceeding the limit, which are available with a range of different properties and characteristics, such as velocity, spin, and compression. Thus, a variety of different balls are available to meet the needs and desires of a wide range of golfers.
Regardless of the form of the ball, players generally seek a golf ball that delivers maximum distance, which requires a high initial velocity upon impact. Therefore, in an effort to meet the demands of the marketplace, manufacturers strive to produce golf balls with high initial velocities.
As a result, golf ball manufacturers are continually searching for new ways in which to provide golf balls that deliver the maximum performance for golfers at all skill levels, and seek to discover compositions that provide the performance of a high compression ball with lower compression.
The physical characteristics of a golf ball are determined by the combined properties of the core, any intermediate layers, and the cover. These, in turn, are determined by the chemical compositions of each. The composition of some balls will provide for increased distance. Other compositions provide for improved spin. Manufacturers are constantly looking to develop the ideal materials. Thermoplastic polyurethane urea for example, have been examined for their innate ability to provide material having very high tensile strengths, which is a very desired property in the make-up of a golf ball.
Segmented polyurethanes are elastomers with a solvent base. They can be processed by methods that involve combining an aromatic polyetherurethane urea with a soft segment of polycarbonate and a hard segment of diphenylmethane diisocyanate and mixed diamines. Hard segments are usually the reaction product of an aromatic diisocyanate and a low molecular weight, chain-extending dialcohol or diol. Soft segments may be synthesized from polycarbonate polyols with terminal hydroxyl (xe2x80x94OH) groups. The hydroxyl creates a urethane group, while the reaction between isocyanates and existing urea groups will form allophanate groups that can produce minor amounts of covalent cross-linking. When heated, the hydrogen-bonded hard segments and any allophanate cross-links, dissociate to allow the polymer to melt and flow. Dissolution in a polar solvent can also disrupt the hydrogen bonds that hold together the hard segments on adjacent chains. Once these virtual cross-links are broken, the polymer can be fabricated into golf ball layers. Upon cooling or solvent evaporation, the hard segments de-mix from the soft segments to re-associate by hydrogen bonding. This restores the original mechanical properties of the thermoplastic elastomer. Conventional segmented polyurethanes generally have excellent physical properties, combining high elongation and high tensile strength, but they are a solvent by nature. By reacting a primary amine first with the isocyanate to form a secondary amine and then the remaining hydrogen on the secondary amine can react a second time with another isocyanate moiety to form a tertiary amine. This second reaction forms a cross-link, which leads to a thermoset material. Secondary amines cannot form secondary reactions, therefore, the urea group does not react with additional isocyanate to form cross-links, and the product is a thermoplastic, which is amine cured.
Therefore, there exists a need for a golf ball comprising a segmented polyurethane for improved golf ball performance. By varying the urea hard segment during synthesis a whole family of polymers of related-chemistry can be produced having a wide range of hardness, modulus, tensile-strength properties and elongation.
The invention is related to a use of a segmented polyurethane comprising urea in the hard segment for the formation of a golf ball core, cover, or intermediate layer.
A first embodiment is a golf ball comprising a core and a cover, at least one of which is formed from a segmented polyurethane comprising an aromatic urea hard segment and a polycarbonate based soft segment. BioSpan(copyright) C, is an example of a suitable segmented polyurethane material and is commercially available from the Polymer Technology Group, Inc.
Another embodiment of the invention incorporates a segmented polyurethane comprising on aromatic urea hard segment and a polyether based soft segment. An example is BioSpan(copyright) SPU, which is a registered trademark for a segmented polyurethane material commercially available from the Polymer Technology Group, Inc.
Most preferable, the segmented PU of the invention is an intermediate layer. Other embodiments of the invention blend the block copolymer of polycarbonate-polyurea with at least one thermoplastic or thermoset polymer including ionomers and copolymers including highly neutralized polymers, epoxies, styrenic and olefinic homo- and copolymers (including metallocenes and single-site); polyamides; polyesters; polydienes; block copolymers of polyether (or ester)-ester and polyether (or ester)-amides. Examples of these may be found in U.S. patents issued to Ward et al. U.S. Pat. Nos. 4,675,361; 5,428,123; 5,589,563; and 5,863,627, Li et al. U.S. Pat. No. 5,221,724; and Leir et al. U.S. Pat. No. 5,461,134, which are incorporated by reference herein in their entirety.
The invention is preferably a two-piece or a multi-layered golf ball having a coefficient of restitution greater than about 0.7 and measured at an incoming velocity of 125 ft/s, and an Atti compression of at least about 50. The intermediate layer is the preferred use of the invention, and comprises segmented polyurethane such that it has a material tensile strength of greater than about 3,000 psi.
Surface modifying end groups (SMEs) are surface-active oligomers covalently bonded to the base polymer during synthesis. The invention can include SMEs that will control surface chemistry without compromising the bulk properties of the polymer. Key surface properties, such as abrasion resistance, are permanently enhanced without additional post-fabrication treatments or topical coatings.